Many portable electronic devices include displays for displaying various types of images. Examples of such displays include electrowetting displays (EWDs), liquid crystal displays (LCDs), electrophoretic displays (EPDs), light emitting diode displays (LED displays), etc. For example, in EWD applications, an applied voltage is utilized to change the surface tension of a liquid in relation to a surface. For instance, by applying a voltage to a hydrophobic surface via a pixel electrode in conjunction with a common electrode, the wetting properties of the surface can be modified so that a second liquid has a greater affinity for the surface. Thus, the quality of the surface is important for operation of the EWD. One way to determine quality of a surface is by measuring a contact angle of a drop of liquid on a surface. The contact angle is the angle, conventionally measured through the liquid, where a liquid/vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation, 0=γSG−γSL−γLG cos θC, where the solid-vapor interfacial energy is denoted by γSG, the solid-liquid interfacial energy is denoted by γSL the liquid-vapor interfacial energy (i.e. the surface tension) is denoted by γLG, and the equilibrium contact angle is denoted by θC.
Conventional contact angle measurement generally involves the use of a goniometer that utilizes a single, charge-coupled device (CCD) camera or a digital camera to obtain images of a droplet on an interface, such as, for example, a substrate surface, to measure the dynamic angle of a liquid on the interface. The contact angle is measured by mounting a CCD camera perpendicular to a liquid droplet to observe the wetting behavior and make sure that a reference needle of the goniometer is in the center position with respect to the droplet when measuring the contact angle. Generally, such conventional methods have a disadvantage in that only one-dimensional calibration is provided, i.e. along an X direction, which results in the observer only seeing the needle centered along the X direction while along the Y direction, the needle may not be properly centered with respect to the droplet. For example, FIG. 1A illustrates a liquid droplet 100 on a substrate 102 viewed along the X direction where a dispensing needle 104 is centered with respect to the liquid droplet 100. However, if the substrate 102 is rotated 90 degrees, it can be seen in FIG. 1B that the needle 104 is not centered with respect to the liquid droplet 100 viewed along the Y direction. Such misalignment of the needle 104 generally affects the results of the contact angle measurement since the camera focuses on the needle 104 when obtaining images for the contact angle measurements.